class_docstr: This class returns normalisation and augmentation layers for use with reader objects.
docstr: returns list of normalisation layers
docstr_tok: ["returns","list","of","normalisation","layers"]
code: def prepare_normalisation_layers(self):
      """
      returns list of normalisation layers
      """
      foreground_masking_layer = None
      if self.net_param.normalise_foreground_only:
          foreground_masking_layer = BinaryMaskingLayer(
              type_str=self.net_param.foreground_type,
              multimod_fusion=self.net_param.multimod_foreground_type,
              threshold=0.0,
          )
  
      mean_var_normaliser = MeanVarNormalisationLayer(
          image_name="image",
          binary_masking_func=foreground_masking_layer,
      )
      histogram_normaliser = None
      if self.net_param.histogram_ref_file:
          histogram_normaliser = HistogramNormalisationLayer(
              image_name="image",
              modalities=vars(self.task_param).get("image"),
              model_filename=self.net_param.histogram_ref_file,
              binary_masking_func=foreground_masking_layer,
              norm_type=self.net_param.norm_type,
              cutoff=self.net_param.cutoff,
              name="hist_norm_layer",
          )
      normalisation_layers = []
      if self.net_param.normalisation:
          normalisation_layers.append(histogram_normaliser)
      if self.net_param.whitening:
          normalisation_layers.append(mean_var_normaliser)
      return normalisation_layers
  
file_path: NiftyNet/niftynet/contrib/preprocessors/preprocessing.py
imports: from niftynet.layer.mean_variance_normalisation import MeanVarNormalisationLayer
  from niftynet.layer.rand_flip import RandomFlipLayer
  from niftynet.layer.rand_rotation import RandomRotationLayer
  from niftynet.layer.rand_spatial_scaling import RandomSpatialScalingLayer
  from niftynet.layer.binary_masking import BinaryMaskingLayer
  from niftynet.layer.histogram_normalisation import HistogramNormalisationLayer
label_desc: Use image node_id 2 for calling the Preprocessing obj's underlying member method code with example usage: obj.prepare_normalisation_layers() and returns: normalisation_layers